This invention relates to contrast enhancement agents for use in magnetic resonance imaging, more particularly to metal chelating ligands and metal chelate compounds useful in the preparation of such contrast enhancement agents.
Magnetic resonance (MR) imaging has become a critical medical diagnostic tool in human health. The use of MR contrast enhancement agents in MR imaging protocols has proven to be a valuable addition to the technique by improving both the quality of images obtained in an MR imaging procedure and the efficiency with which such images can be gathered. Known MR contrast enhancement agents suffer from a variety of deficiencies. For example, MR contrast enhancement agents containing gadolinium (Gd) chelates, while themselves are not toxic comprise gadolinium ion which in free ionic form is toxic. Contrast enhancement agents comprising chelates of manganese (Mn) may be subject to dissociation of the chelating ligand from the manganese metal center which is undesirable. Various other metal chelates may serve as MR contrast enhancement agents but are frequently less effective than gadolinium chelates and/or are not cleared from the body of the subject at sufficiently high rates following the imaging procedure.
Considerable effort and ingenuity has been expended to reduce the latent toxicity and control bio-distribution of MR contrast enhancement agents comprising gadolinium chelates. Potential MR contrast enhancement agents should exhibit good in-vivo and in-vitro stability, as well as prompt clearance from the body following an MR imaging procedure. MR contrast enhancement agents comprising a paramagnetic iron center are attractive because iron has an extensive and largely innocuous natural biochemistry as compared to gadolinium. This has led to increased interest in the use of iron-based materials as contrast agents for MR imaging.
There exists a need for additional iron-containing contrast enhancement agents for MR imaging that exhibit performance superior to or equivalent to known contrast enhancement agents while providing one or more additional advantages, such as improved image quality at lower patient dosages, greater patient tolerance and safety when higher doses are required, and improved clearance from the patient following the imaging procedure.